Transient disruption of T cell help impairs germinal center dynamics and memory responses

T follicular helper (T FH ) cells are essential for germinal center (GC) formation and long-lived humoral immunity. Here, we used an Il21 fate mapping (Il21-fm) strategy to remove T FH cells from established GCs to disentangle their function from that of other T cells in a temporal manner. We confirm their role in driving proliferation and positive selection of GC B cells but show that GCs can survive the transient absence of T FH cells. After ablation of T FH cells, both the GC response and affinity maturation recover via ingress of new T FH cells. Despite recovery of the B cell response, T FH cell numbers are never fully restored. This feeds through into the T cell memory response, resulting in diminished recall GC responses. This work shows an unappreciated resilience of primary GC responses to perturbations in T FH cells and demonstrates critical memory T cell generation during this phase.